Charging blast holes with explosive



2 Sheets-Sheet l F'ild July 27, 1955 H V 5 H RHC Y oW E T I 4% J w w M A E G. H. SMITH ETAL CHARGING BLAST HOLES WITH-EXPLOSIVE March 29, 1960 2 Sheets-Sheet 2 Filed July 27, 1.955

INVENTORS H. SMITH IAM J. MITCHELL fi ('T%RNEY-) UnitedStates Patent 2,930,276 I CHARGING BLAST HOLES wmr ExrLosivn 2 Claims. (Cl. 86- 20) The present invention relates to the charging of blast holes with explosive of the liquid oxygen type.

-Heretofore, many processes have been proposed for charging blast holes with explosives of the liquid oxygen type, but all such processes presentfinherent difficulties which affect either the speed andjefliciency of charging, the protection of the Operator from the danger of possible premature explosions, or the provision of a charge in'the hole which can' be leftuntil lateruse is desired; j V

One prior process'proposes charging the blast hole with a plurality of bags of liquid oxygen-soaked carbonaceous combustible material. In this process the bags of combustible material, such as carbon, were soaked inliquid oxygen by the operator and charged into the blast hole one after the other until a desired total charge was provided. Tamping of the bags was required and difliculties were continuously encountered due to the irregularities in the side walls of the blast hole, particularly where deep rock pierced blast holes of the type encountered in] the taconite mining fields were to be charged. In addition, the handling of mixed carbon and liquid oxygen at the surfaceby the operator presented a serious safety problem. f

Deep, drilled or jrock pierced blast holes present the additional problem of leakage of seepage water into the hole through cracks and fissures in the side walls of the hole. Should any considerable time elapse between the charging of the hole and the ignition of the charge, the problem of flooding the charge with seepage water, entering the hole through the cracks and'fi's sures, may be encountered.

' In an effortto solve this seepage water'problem, it has been proposed to freeze the side walls of the hole with a ,coldliquefied gas prior to charging the h'olef'with an explosive of the liquid oxygen typef Such a procedure is capable of providinga charged blast hole which can be allowed to stand for only relatively short periods of time prior to ignition due to the fact'that the frozen walls of the blast hole can "be" so maintained for only relatively short periods of time. It has been found in blasthole forming and charging operations that the most economical and eflicient procedure is to charge each hole soon after ithas been formed, and to sov form and charge a series of holes before any blasting isperformed. This procedure, therefore, requires that a blast hole be left charged or semicharged for relatively long periods of time, of the order of days, beforeblasting operations are begun. It can be seen that the wall-freezing processtdescribed hereinabove would not sufiice to. protect the charge from seepage water for such an extended period of time.

Another process has been proposed employing an elongated, inflatable, impervious tube which is first inserted into the hole, inflated with inert gas, and into which a freely-flowing liquid oxygen explosive mixture is dispensed from a dispenser positioned at the surface of the hole, While such a process provides a method of charg- "ice ing blast holes rapidly, the process presents an inherent safety problem in that the mixture of carbon and liquid oxygen is formed at the surface of the hole, thereby introducing the ever present possibility of premature explosion of the mixture at that point, and protracted delays in time before blasting cannot be tolerated.

Accordingly, it is the prime object of the present invention to provide a method for charging blast holes with explosives of the liquid oxygen type wherein no mixing of the combustible material and liquid oxygen is effected prior to introduction into the hole.

Other aims and advantages of the present invention will be apparent from the following description and appended claims.

In the drawings:

Fig. 1 is an elevational sectional view of apparatus capable of charging a blast hole in accordance with the method of the invention, the blast hole being shown in the uncharged condition;

Fig. 2 is an elevational sectional view similar to that of Fig. l, the blast hole being shown in the charged condition; and

Fig. 3 is a partial sectional view showing details of construction of an inflatable bag arrangement employable in the practice of the method of the invention.

In accordance with the present invention, a method is provided for charging blast holes with explosive of the liquid oxygen type comprising the steps of: lowering an elongated, collapsed, inflatable, expansible bag of substantially impervious material into the blast hole, running a small tube (carrying conventional detonating means) inside of the bag to a point near the bottom of the hole, inflating the bag with a gas, blowing agglomerates of a combustible material into the inflated bag around the small tube, stemming the'unfilled remainder of the bag, and then introducing liquid oxygen into the bag through the small tube to mix with and soak the combustible material previously deposited therein. The combustible material and stemming may be charged in alternate layers if desired to produce "deck loading ofthe explosive charge.

More specifically and referring to Fig. 1 of the drawings, an'elongated impervious bag 10 of inflatable material having a weighted lower end portion 12 is lowered into the blast .hole 14 to be charged until the weighted lower end portion 12 reaches the bottom of the hole. Bag 10 should have a diameter at least as large as the largest pocket or convolution in the side walls of the blast hole 14 to permit filling of the entire hole upon expansion. A small'narrow tube 16 of suitable material is passed into the hole 14 within bag 10 to a point near the lower end of bag 10. Conventional detonator meansand connecting wires (not shown) may be attached to the outside of tube 16 at any desired point or points to control the explosion.

Bag 10 is inflated with any suitable nonreactive gas, such as compressed air, entering the bag through inlet conduit means 18 from a gas source 20, such as the air compressor positioned on truck 22. Gas outlet conduit 24 is also provided, together with relief valve means 26, to regulate the gas pressure within the bag 10. The introduction of inflating gas'into the bag displaces any water within the hole so that the bag substantially contours and fills the hole. A particulated combustible material 30, such as'carbon,is then fed into the hole within the bag to the desired capacity and may be so carried in a stream of gas such as compressed air, from hopper 32 through gas inlet conduit means 18 by the proper adjustment of valves 34. Upon charging the hole with such agglo'merate combustible material 30, the remainder of the hole above the agglomerate is filled with a suitable stemming material 36, such as gravel, crushed rock, and

the like. At this point the hole will be charged, as shown in Fig. 2 of the drawings, to the ground level leaving only tube 16 and detonator means connecting wires (not shown) exposed and passing from the top of the hole.

When it is desired to carry out the. blasting operation, the charging of the hole is completed by the introduction of liquid oxygen from a dispensing container 3 8 into the hole through small filler tube 16. The liquid oxygen discharged into the lower end of the hole in this manner serves to soak the combustible material agglomerate pro gressively upwards within the hole and thereby form the liquid oxygen explosive. v

The introduction of liquid oxygen into the hole after stemming has been completed permits the retaining of agglomerate combustible material within the hole. the stemming were not employed as a restraining filter in this manner, the evaporated oxygen gas would flui-dize the agglomerate combustible material and blow it out the top of the hole.

It has been found that the elongated, impervious, expansible bag 10 may be composed of a wide variety of materials, such as plastic, paper, and the like. It has been found advantageous that the bag 10 be covered with an outer layer, such as cloth, burlap, and the like, to protect it from tearing on the rough inner surface protrusions of the blast hole. A particularly suitable. combination for the bag was found to consist of polyethylene terephthalate plastic, 0.061 inch thickness encased in 14 ounce burlap.

Small liquid oxygen filler tube 16 may be composed of any material capable of handling liquid oxygen at the low temperatures involved, such as metal and even cardboard or a rigid plastic material, and, since such tubes must of necessity be replaced after each blasting operation, a cheap and readily available cardboard material may be advantageously employed.

The introduction of liquid oxygen into the charge of agglomerate of combustible material at the bottom of the hole provides two very advantageous results: first, it prevents vapor lock and slow soaking rates that occur when the liquid is introduced at the top of the agglomerate charge; secondly, it allows the oxygen gas vapor gencrated at the soaking interface to pass upwardly through the uncoo'led portions of the agglomerate charge. The soaking is thus smooth and rapid because the agglomerate charge is precooled before liquid contact and, in this manner, practically all the refrigeration available in the oxygen gas is recovered since the gas escapes at about atmospheric temperature.

It has been found preferably that the combustible material agglomerate have a particle size in the range of from approximately 4 to 16 mesh. Particles larger than about 4 mesh are to be avoided to prevent bridging in the conveyor tubing and particles finer than about 16 mesh are to be avoided to permit an adequate flow of gas through the charge at an acceptable pressure drop.

Referring specifically to the embodiment shown in Fig. 3 of drawings, plastic bag 10 is provided having an outer closing fiber bag 40 having a lower end weighted with gravel 42 or the like. Upper closure assembly 44 and lower plug 46 are provided to retain the ends of the elongated bag 10 and are composed of metal, wood, or other suitable material. Upper closure assembly 44 is provided with means for assuring gas-tight connections between each of conduit-s 18, 16 and 24 and the interior of bag 10. Lower plug 46 is likewise made liquid tight.

What is claimed is:

1. The method of charging a blast hole with explosive of the liquid oxygen type comprising lowering an elongated collapsed and weighted inflatable bag of substantially impervious material into said hole; passing a liquid oxygen filling tube into said hole through said bag to a point near the bottom thereof; inflating said bag with a gas under controlled pressure so that said bag substantially contours and fills said hole; inserting charge-detonating means in the inflated bag; dispensing into said gasinflated bag in a carrier gas stream at above atmospheric pressure, agglomerates of carbonaceous combustible material having agglomerate particle sizes between approximately 4 mesh and 16 mesh to charge said hole to a desired depth; simultaneously maintaining the bag in the inflated state to fill said hole, by regulating the internal bag pressure at above atmospheric; stemming the remaining uncharged portion of said hole with gravel; and at any time thereafter, dispensing liquid oxygen through such filling tube into the bottom of said charge of combustible material in quantity suflicient to cool the combustible material and then convert such material into an explosive charge and at a rate such that the vapors of the liquid oxygen vaporized by heat exchange with the combustible are released to thesurface by upward flow first through the combustible agglomerates to progressively precool them before progressive liquid contact and then through the gravel stemming material for escape at substantially atmospheric temperature.

2. The method of charging a blast hole with explosive of the liquid oxygen type comprising lowering an elongated collapsed and weighted inflatable bag of substantially impervious material into said hole, passing a liquid oxygen filling tube into said hole through said bag to a point near the bottom thereof; inflating said bag with a gas under controlled pressure so that said bag substantially contours and fills said hole; dispensing into said gas-inflated bag in a carrier gas stream at above atmospheric pressure, agglomerates of carbonaceous combustible material having agglomerate particle sizes between approximately 4 mesh and 16 mesh to charge said hole to a desired depth; simultaneously maintaining the bag in the inflated state to fill said hole, by regulating the internal bag pressure at above atmospheric; stemming the remaining uncharged portion of said hole with gravel; and at any time thereafter, dispensing liquid oxygen through such filling tube into the bottom of said charge of combustible material in quantity suflicient to cool the combustible material and then convert such material into an explosive charge and at a rate such that the vapors of the liquid oxygen vaporized by heat exchange with the combustible are released to the surface by up ward flow first through the combustible agglomerates to progressively precool them before progressive liquid contact and then through the gravel stemming material for escape at substantially atmospheric temperature.

References Cited in the file of this patent UNITED STATES PATENTS 371,298 Bourne Oct. 11, 1887 1,565,766 Weber Dec. 15, 1925 2,609,750 McFarland Sept. 9, 1952 2,704,515 Barlow Mar. 22, 1955 2,745,346 Aitchison et al. May 15, 1956 2,879,149 Brown Mar. 24, 1959 FOREIGN PATENTS 217,169 Great Britain June 26, 1924 1,055,280 France Oct. 14, 1953 725,371 Great Britain Mar. 2, 1955 

1. THE METHOD OF CHARGING A BLAST HOLE WITH EXPLOSIVE OF THE LIQUID OXYGEN TYPE COMPRISING LOWERING AN ELONGATED COLLAPSED AND WEIGHTED INFLATABLE BAG OF SUBSTANTIALLY IMPERVIOUS MATERIAL INTO SAID HOLE, PASSING A LIQUID OXYGEN FILLING TUBE INTO SAID HOLE THROUGH SAID BAG TO A POINT NEAR THE BOTTOM THEREOF, INFLATING SAID BAG WITH A GAS UNDER CONTROLLED PRESSURE SO THAT SAID BAG SUBSTANTIALLY CONTOURS AND FILLS SAID HOLE, INSERTING CHARGE-DETONATING MEANS IN THE INFLATED BAG, DISPENSING INTO SAID GASINFLATED BAG IN A CARRIER GAS STREAM AT ABOVE ATMOSPHERIC PRESSURE, AGGLOMERATES OF CARBONACEOUS COMBUSTILE MATERIAL HAVING AGGLOMERATE PARTICLE SIZES BETWEEN APPROXIMATELY 4 MESH AND 16 MESH TO CHARGE SAID HOLE TO A 